Project Summary/Abstract The long-term goal of this research program is to develop cost-effective strategies to increase moderate- intensity physical activity (PA) among sedentary women. Fewer than half of U.S. women meet recommendations for moderate-intensity PA, and thereby are at increased risk for cardiovascular disease. When provided a PA program, between 25-60% of women either fail to adopt it or fail to adhere after six months. PA health benefits are further negatively impacted by the fact that sedentary behavior at many worksites exacerbates low PA. Among efficacious treatments for increasing PA for women, four have had promising results: (1) enhanced PA monitor treatment (PA monitor with goal setting and a PA prescription); (2) motivational text messages; (3) motivational personal calls; and (4) group meetings. While each of these treatments has proven efficacy, they differ on resource use and cost, and there is heterogeneity in response. When treatments have heterogeneity of response, adaptive interventions can help close that gap. Adaptive interventions start with an initial treatment and then transition to an augmented treatment for non-responders. This study aims to determine the most effective adaptive intervention combining four efficacious treatments (enhanced PA monitor, motivational text messages, motivational personal calls, group meetings) to increase PA (step counts per day, minutes moderate/vigorous PA per week) and improve cardiovascular health (aerobic fitness, body composition) among sedentary employed women. We will also assess treatment effects on intervention targets (PA benefits, PA barriers, PA self-efficacy, and social support). A Sequential Multiple Assignment Randomized Trial (SMART) design will address the following aims: 1) Among non-responders to the initial treatments (enhanced PA monitor and enhanced PA monitor+ motivational text messages), compare the two augmented treatments (motivational personal calls and group meetings); 2a) Compare the two initial treatments and; 2b) Compare the four adaptive interventions embedded in the SMART on PA and cardiovascular health; 3) Identify mediators and moderators of the initial and augmented treatments on PA and cardiovascular health; 4) Compare the cost-effectiveness of the four adaptive interventions from the societal perspective which includes both program costs and participant costs. We will recruit 312 sedentary women, aged 18 to 65, who are employed at a large urban academic medical center. Data will be collected on PA (self- report, device), cardiovascular health, PA benefits, PA barriers, PA self-efficacy, social support, and program and participant costs. Data will be collected at baseline, weeks 9-10 (when response to initial treatment is assessed), weeks 34 -35, and weeks 51-52. We expect to identify an optimal adaptive intervention for improving PA and cardiovascular health that minimizes costs and burden to women who respond to less intensive treatments, while maximizing benefits for those who need a more intensive approach.